The subject matter disclosed herein relates generally to gas turbine engines, and, more specifically, to active clearance control systems for gas turbine engines.
In some gas turbine engines, such as those used to propel aircraft, some aspects of engine performance may depend upon clearances between turbine blade tips and static seals or shrouds surrounding the blade tips. For example, excessive blade tip clearances may adversely affect thrust, specific fuel consumption, and/or exhaust gas temperature margin.
Some gas turbine engines may use active clearance control to adjust turbine blade tip clearances at various engine operating conditions. For example, some active clearance control systems may be configured to direct relatively cool or relatively hot air, which may be generally referred to as thermal control air, onto high or low pressure turbine casings to cause the casings to thermally expand away from the blade tips (increasing the tip clearances) or contract (reducing the tip clearances).
The problems: Some active clearance control systems may be ineffective at controlling blade tip clearances due to limited heat transfer capacity and/or some active clearance control systems may adversely affect engine performance due to their use of relatively large amounts of thermal control air.